Arrangement for producing artificial reverberation comprising frequency dividing means

ABSTRACT

An artificial reverberation arrangement includes first and second transmission lines. Each transmission line includes a helical spring, adapted to transmit torsional vibrations at frequencies up to a predetermined limiting frequency, an actuating transducer connected to one end of the spring and a pickup transducer connected to the opposite end of the spring. The spring of the first transmission line is longer, and has a longer transit time and a lower limiting frequency, than the spring of the second transmission line. The actuating transducers are operable to impart torsional vibrations to the associated springs, and the pickup transducers are operable to convert torsional vibrations of the respective springs and to electric oscillations. The arrangement includes frequency dividing means operable to suppress transmissions above a predetermined division frequency through the first transmission line, and to suppress transmission at frequencies below the predetermined division frequency through the second transmission line.

United States Patent [72] Inventors Bernhard Weingartner;

Werner Fidi, both of Vienna, Austria [21 1 Appl. No.

[22] Filed Dec. 3, 1968 [45] Patented June 22, 1971 I 73] AssigneeAkusthclae u-Kino Gerate Gesellschaft m.b.II

Vienna, Austria [32] Priority Dec. 7, 1967 [3 3 l Austria [3 l 1 Al 1100/67 [54] ARRANGEMENT FOR PRODUCING ARTIFICIAL REVERBERATIONCOMPRISING FREQUENCY 3,150,335 9/1964 Schreier' ABSTRACT: An artificialreverberation arrangement includes first and second transmission lines.Each transmission line includes a helical spring, adapted to transmittorsional vibrations at frequencies up to a predetermined limitingfrequency, an actuating transducer connected to one end of the springand a pickup transducer connected to the opposite end of the spring. Thespring of the first transmission line is longer, and has a longertransit "time and a lower limiting frequency, than the spring of thesecond transmission line. The actuating transducers are operable .toimpart torsional vibrations to the associated springs, and the pickuptransducers are operable to convert torsional vibrations of therespective springs and to electric oscillations. The arrangementincludes frequency dividing means operable to suppress transmissionsabove a predetermined division frequency through the first transmissionline, and to suppress transmission at frequencies below thepredetermined division frequency through the second transmission line.

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ARRANGEMENT FOR PRODUCING ARTIFICIAL REVERBERATION COMPRISING FREQUENCYDIVIDING MEANS BACKGROUND OF THE INVENTION Various arrangements forproducing artificial reverberation have been disclosed, and arrangementsincluding helical springs, to which torsional vibration is imparted,have found the widest use. Torsional vibration is imparted to thehelical springs, preferably at one end thereof, by electromechanicalmeans, and is reconvened into electrical oscillation by a pickuptransducer which is connected at the other end of the springs.

Reverberation is produced due to the fact that the signal to bereverberated, which is a propagated along the helical spring or springs,is delayed relative to the original signal which is directly amplified,and because the signal to be reverberated is partly subjected tomultiple reflection within the helical spring or springs, which areterminated at opposite ends by respec tive transducers. This reflectioncauses a fading of the signal, due to internal friction.

To produce a reverberation of maximum fidelity, the helical spn'ngshould have the same properties, with respect to transit time,reflection and damping, as a reverberating space. As this requirementcan be met to only a certain extent, due to different physicalconditions, artificially produced reverberation can be distinguishedclearly from natural reverberation. Even if a plurality of springshaving respective different transit times are employed, the resultingimprovement will be accompanied by disturbing effects, which are absentin naturally reverberated sound.

There have been proposed spring assemblies comprising either one springor several springs connected in parallel. Where two springs areemployed, the associated transit times are, in most cases, 5080milliseconds and -40 milliseconds, respectively. This is a compromisebetween a high frequency response with minimum frequency intervalsbetween the natural resonance frequencies and a dense pulse spectrum(large frequency intervals between the natural resonance frequencies).Both of these results cannot be achaving the short transit time wereomitted, the reverberation effect would be good, but disturbing echoeswould result and would be heard clearly in addition to the reproductionof the original sound. These echoes are highly disturbing.

SUMMARY OF THE INVENTION This invention relates to means for producingartificial reverberation and, more particularly, to a novel means forthis purpose which is free of disadvantages of prior art means orarrangements, as set forth above.

More specifically,an arrangement forproducing artificial reverberationin accordance with the invention comprises at least two delay elementsconsisting of helical springs which differ in length and transit timeproperties and which are adapted to have torsional vibration impartedthereto. Each helical spring has associated with it separate actuatingand pick up transducers, which are preferably of the electrodynamictype. The signal to be transmitted and rever berated is applied to thehelical springs by mechanical or electrical devices or arrangements, orboth, which have a frequency range dividing effect with respect to adivision frequency which is approximately the same as the limitingfrequency of the helical spring having the longer transit time. Only thefrequencies below its limiting frequency are transmitted by or suppliedto the helical spring having the longer transit time, and only thehigher frequencies, preferably up to the limiting frequency of thehelical spring having the shorter transit time,

are transmitted by or supplied to the latter spring. The divisionfrequency is preferably in the middle of the frequency range of thesound to be reverberated.

In this connection, the term limiting frequency" refers to the upperlimit of the frequency range in which torsional vibrationv can betransmitted by a helical spring, whereas preferably only compressionalvibration and possibly transverse vibration is transmitted atfrequencies above the limiting frequency.

The limiting frequency f,,, in cycles matically defined by the equationThe transit time Tin seconds is calculated by the equation In the twoequations, a is the radius of the spring wire in meters, R is the meanspring radius in meters, E is the modulus of elasticity in kilograms persquare meter, and p is the density of the spring material in kilogramsper cubic meter. K and K are specific constants which must be determinedindividually for each spring with respect to a given spring material, agiven initial spring tension, and a given spring uniformity, and w isthe number of turns of the spring.

For a given dividing frequency and desired transit time, each of the twohelical springs can be designed so as to meet the requirements of theinvention.

The invention arrangement has the advantage that the frequency rangewhich is to be transmitted and to be reverberated is divided between twohelical springs which are actuated only at frequencies at which puretorsional vibration is transmitted. The inherent short transit time ofthe smaller spring does not result in a loss of quality. On thecontrary, the small delay of the trebles relative to basses has theresult that the first echo cannot be perceived if the division frequencyor the natural frequency of the spring having the longer transit persecond, is mathetime lies between 3 and 4 kilocycles per second. Theinvention results in an improved reverberation effect as compared toknown arrangements, and also in a reduction of the size of thearrangement because, for a given diameter of the spring wire, areduction of the limiting frequency of the spring by a factor of 0.5results, for a given transit time, in a reduction of the length of thespring by a factor of 0.25.

The division of the frequency range to be transmitted or reverberatedmay be effected by mechanical means, by electrical means, or by both. Afeature of the mechanical means, in accordance with the invention, isthat the means suspending the helical spring having the longer transittime at either the actuating end, the pickup end, or both ends, has asmall damping effect on torsional vibration but is stiff and has a largedamping effect for compression waves. At least one of the suspendingmeans for the spring having a shorter delay time assures that thisspring transmits torsional vibrations above the division frequency.

Where rotary magnets are used to actuate the helical springs and to pickup vibrations therefrom, it is sufficient if the suspending means forthe helical spring having the longer transit time comprises essentiallya piece of wire which is soft in respect to torsional vibration, butpresents a resistance to compressional vibration. The. rotary magnet,preferably that of the actuating transducer, is embedded in foammaterial, which suppresses compressional vibration. The spring havingthe shorter transit time is suspended at one or both ends by a short,stiff piece of wire, and the rotary magnets are also embedded in foammaterial, if desired.

The frequency division may be effected by electrical means. Thus, inaccordance with the invention, a filter circuitry may be included in theinput circuit, the output circuit, or both circuits associated with eachspring, and the filter circuitry associated with the spring having thelonger transit time has a pass band up to the limiting frequency of thespring. The filter circuitry associated with the shorter spring has apass band from the division frequency up to the limiting frequency ofthe shorter spring. A particularly effective frequency division can beaccomplished by the combination of electrical and mechanical filtercircuits.

An object of the present invention is to provide an improved arrangementfor producing artificial reverberation. Another object of the inventionis to provide such an arrangement including two helical springs, actingas delay elements, and which differ in length and transit timeproperties,'each of the helical springs being arranged to have torsionalvibration imparted thereto.

A further object of the invention is to provide such an arrangement inwhich each helical spring has associated therewith separate actuatingand pickup transducers.

Another object of the invention is to provide such an arrangement inwhich the transducers are preferably of an elec trodynamic type. I

A further object of the invention is to provide such an arrangement inwhich the signal to be transmittedand reverberated is applied to thesprings by mechanical, electrical, or combined mechanical and electricaldevices having a frequency range dividing effect with respect to adivision frequency which is approximately the same as the limitingfrequency of the helical spring having the longer transit time. Anotherobject of the invention is to provide such an arrangement in which onlythose frequencies below its limiting frequencies are transmitted by, orsupplied to, the helical spring having the longer transit time.

A further object of the invention is to provide such an arrangementwhere only the higher frequencies, preferably up to the limitingfrequency of the helical spring having the shorter transit time, aretransmitted by or supplied to the helical spring having the shortertransit time.

Another object of the invention is to provide such an arrangement whichhas a division frequency preferably in the middle of the frequency rangeof the sound to be reverberated.

For an understanding of the principles of the invention, reference ismade to the following description of typical embodiments thereof asillustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERREDEMBODIMENTS As has been mentioned above, the essence of the presentinvention resides in that the frequency range to be transmitted or to bereverberated is divided between at least two helical springs, each ofwhich has optimum transmitting qualities for part of the frequencyrange, and that the difference between the delay times of the twofrequency bands has the result that the first echo, as well as flutterechoes, cannot be perceived although a good reverberation effect isproduced.

FIG. 1 illustrates an arrangement comprising two helical springs and inwhich only strictly mechanical means are employed. A longer spring 1introduces, into the transmission path of the reverberating system, alonger transit time in which the delay may amount to 120 milliseconds,for example. The shorter spring 2 is so designed that it delays theimpressed signal by about 60 milliseconds. The transducers which areused are of the dynamic type and are supplied from the source s (I)having the internal resistance R, (t). The drawing shows only thoseparts of the transducers which are directly connected to the helicalsprings.

The illustrated parts include rotary magnets 3 at the actuating end androtary magnets 4 at the pickup end. In accordance with the invention,these magnets are connected by respective wire elements to a fixed partof the reverberating device. Wire elements 5 are relatively long andpresent a very high resistance to a movement in an axial direction,whereas they have virtually no effect on torsional motions. In addition,rotary magnets 3 and 4 are embedded in damping material 6, such as afoam material, so that residual compressional vibration will be dampedwhereas this damping will not have any substantial effect on torsionalvibration.

The suspending means for the shorter spring 2, which has a shortertransit time, must have an adequate stiffness for torsional vibration,and consists, for example, of a relatively thick and short wire member 7which is guided centrally.

The electric output signals from the two pickup systems are delivered torespective transducers connected to an audio frequency transformer 14having two primary windings and a single secondary winding. Transformer14 is connected to the input of a further amplifier (not shown), and canbe coupled through the latter, into the main amplification path.

In the reverberating device embodying the invention, as illustrated inFIG. 2, electric means are used to divide the frequency range to betransmitted or reverberated. In the same manner as for the embodimentshown in FIG. 1, the two helical springs are designed in accordance withthe principles set forth above. The electric filter circuitry mayconsist substantially of high pass and low-pass filters, and may precedethe actuating transducers and precede or succeed the pickup transducers.

Referring to FIG. 2, the arrangement illustrated therein includes aninput or dividing amplifier 12 to whose output is connected an electricseparating network consisting of a lowpass filter 8 and a high passfilter 10. The signal to be reverberated is transmitted from the outputof low-pass filter 8 to the actuating transducer for the longerspring 1. In this actuating transducer, the signal is converted intotorsional vibrations which, in a known manner, travel along spring 1 andare reconverted into electric oscillations by a pickup transducer at theother end of spring 1.

The output of high pass filter 10 is supplied to the actuatingtransducer for the shorter spring 2, and after traveling through spring2, the torsional vibration is reconverted into electric oscillations bya pickup transducer. Filter circuits 9 and 11 are connected to thepickup transducers which are connected to the ends of springs 1 and 2,respectively. The outputs of filter circuits 9 and 11 are combined andsupplied to the input of the common amplifier 13 whose output may bereintroduced into the main amplification path, or which may be used toactuate a separate loudspeaker for reverberated sound.

A satisfactory effect generally will be produced if the electricseparating network is provided only at the actuating end. A furtherimprovement may be obtained if the high pass filter is replaced by aband-pass filter, which limits the transmission range of the shorterspring to that range which lies between the two limiting frequencies.

Mechanical and electrical means of the kind described above may becombined, if desired, to provide a reverberating device which issubstantially free of disturbing effects.

What we claim is:

1. An arrangement for producing artificial reverberation comprising, incombination, first and second helical springs each adapted to transmittorsional vibration at frequencies up to a respective predeterminedlimiting frequency, said first spring being longer, and having a longertransit time and a lower limiting frequency, than said second spring;first and second actuating transducers connected to said first andsecond springs, respectively, and operable to impart torsional vibrationto the associated springs; first and second pickup transducers connectedto said first and second springs, respectively, and operable to converttorsional vibration of the associated springs into electricoscillations; said first actuating transducer, first spring and firstpickup transducer constituting a first transmission line; said secondactuating transducer, second spring, and second pickup transducerconstituting a second transmission line; and frequency dividing meansconnected to said transducers suppressing transmission, at frequenciesabove a predetermined division frequency, by said first transmissionline and suppressing transmission, at frequencies below saidpredetermined division frequency, by said second transmission line; saiddivision frequency being substantially equal to the limiting frequencyof said first spring.

2. An arrangement for producing artificial reverberation, as claimed inclaim l,in which said transducers comprise electrodynamic transducers.

3. An arrangement for producing artificial reverberation, as claimed inclaim 1, in which said frequency dividing means comprise mechanicalfrequency dividing means.

4. An arrangement for producing artificial reverberation, as claimed inclaim 1, in which said frequency dividing means comprise electricfrequency dividing means.

5. An arrangement for producing artificial reverberation, as claimed inclaim 1, in which said frequency dividing means comprise mechanical andelectric frequency dividing means.

6. An arrangement for producing artificial reverberation, as claimed inclaim 1, in which said frequency dividing means transmit frequencieswithin a predetermined range; said division frequency beingapproximately in the middle of said range.

7. An arrangement for producing artificial reverberation, as claimed inclaim 1, in which said actuating transducers and said pickup transducersare connected to the associated springs near first and second ends,respectively, of the associated springs; respective suspending meanssuspending said springs at said first and second ends thereof; thesuspending means at one end of said first spring having a small dampingeffect for torsional vibration and being stiff and having a largedamping effect for compressional vibration; at least one of thesuspending means for said second spring suppressing torsional vibrationof said second spring at frequencies below said division frequency.

8. An arrangement for producing artificial reverberation, as claimed inclaim 9, in which said transducers are electrodynamic transducers; thesuspending means at the first end of said second spring comprising apiece of wire which is soft in torsional vibration and presents a highresistance to compressional vibration; at least one of the suspendingmeans connected to said second spring comprising a short stiff piece ofwire extending axially of said second spring.

9. An arrangement for producing artificial reverberation, as claimed inclaim 8, in which said transducers comprise rotary magnets; the rotarymagnet of at least one of said second transducers being embedded in foammaterial adapted to suppress compressional vibration.

10. An arrangement for producing artificial reverberation, as claimed inclaim 9, in which the rotary magnet of at least one of said firsttransducers is embedded in foam material adapted to suppresscompressional vibration.

11. An arrangement for producing artificial reverberation, as claimed inclaim 1, in which said frequency dividing means comprises first andsecond electric filter means connected in said first and secondtransmission lines, respectively.

12. An arrangement for producing artificial reverberation, as claimed inclaim 11, in which each of said electric filter means includes a filterelement preceding the actuating transducer of the respectivetransmission line.

13. An arrangement for producing artificial reverberation, as claimed inclaim 11, in which each of said electric filter means includes a filterelement succeeding the pickup transducer of the respective transmissionline.

14. An arrangement for producing artificial reverberation, as claimed inclaim 11, in which each of said electric filter means includes a filterelement which precedes the actuating transducer and a filter elementwhich succeeds the pickup transducer of the respective transmissionline.

15. An arrangement for producing artificial reverberation,

as claimed in claim 11, in which said second filter means, in saidsecond transmission line, includes a high pass filter having a limitingfrequency which is approximately equal to said division frequency.

16. An arrangement for producing artificial reverberation,

as claimed in claim 11, in which said second filter means, in saidsecond transmission line, suppresses transmission of frequencies outsidethe range defined between the limiting frequencies of said first andsecond springs.

1. An arrangement for producing artificial reverberation comprising, incombination, first and second helical springs each adapted to transmittorsional vibration at frequencies up to a respective predeterminedlimiting frequency, said first spring being longer, and having a longertransit time and a lower limiting frequency, than said second spring;first and second actuating transducers connected to said first andsecond springs, respectively, and operable to impart torsional vibrationto the associated springs; first and second pickup transducers connectedto said first and second springs, respectively, and operable to converttorsional vibration of the associated springs into electricoscillations; said first actuating transducer, first spring and firstpickup transducer constituting a first transmission line; said secondactuating transducer, second spring, and second pickup transducerconstituting a second transmission line; and frequency dividing meansconnected to said transducers suppressing transmission, at frequenciesabove a predetermined division frequency, by said first transmissionline and suppressing transmission, at frequencies below saidpredetermined division frequency, by said second transmission line; saiddivision frequency being substantially equal to the limiting frequencyof said first spring.
 2. An arrangement for producing artificialreverberation, as claimed in claim 1, in which said transducers compriseelectrodynamic transducers.
 3. An arrangement for producing artificialreverberation, as claimed in claim 1, in which said frequency dividingmeans comprise mechanical frequency dividing means.
 4. An arrangementfor producing artificial reverberation, as claimed in claim 1, in whichsaid frequency dividing means comprise electric frequency dividingmeans.
 5. An arrangement for producing artificial reverberation, asclaimed in claim 1, in which said frequency dividing means comprisemechanical and electric frequency dividing means.
 6. An arrangement forproducing artificial reverberation, as claimed in claim 1, in which saidfrequency dividing means transmit frequencies within a predeterminedrange; said division frequency being approximately in the middle of saidrange.
 7. An arrangement for producing artificial reverberation, asclaimed in claim 1, in which said actuating transducers and said pickuptransducers are connected to the associated springs near first andsecond ends, respectively, of the associated springs; respectivesuspending means suspending said springs at said first and second endsthereof; the suspending means at one end of said first spring having asmall damping effect for torsional vibration and being stiff and havinga large damping effect for compressional vibration; at least one of thesuspending means for said second spring suppressing torsional vibrationof said second spring at frequencies below said division frequency. 8.An arrangement for producing artificial reverberation, as claimed inclaim 9, in which said transducers are electrodynamic transducers; thesuspending means at the first end of said second spring comprising apiece of wire which is sOft in torsional vibration and presents a highresistance to compressional vibration; at least one of the suspendingmeans connected to said second spring comprising a short stiff piece ofwire extending axially of said second spring.
 9. An arrangement forproducing artificial reverberation, as claimed in claim 8, in which saidtransducers comprise rotary magnets; the rotary magnet of at least oneof said second transducers being embedded in foam material adapted tosuppress compressional vibration.
 10. An arrangement for producingartificial reverberation, as claimed in claim 9, in which the rotarymagnet of at least one of said first transducers is embedded in foammaterial adapted to suppress compressional vibration.
 11. An arrangementfor producing artificial reverberation, as claimed in claim 1, in whichsaid frequency dividing means comprises first and second electric filtermeans connected in said first and second transmission lines,respectively.
 12. An arrangement for producing artificial reverberation,as claimed in claim 11, in which each of said electric filter meansincludes a filter element preceding the actuating transducer of therespective transmission line.
 13. An arrangement for producingartificial reverberation, as claimed in claim 11, in which each of saidelectric filter means includes a filter element succeeding the pickuptransducer of the respective transmission line.
 14. An arrangement forproducing artificial reverberation, as claimed in claim 11, in whicheach of said electric filter means includes a filter element whichprecedes the actuating transducer and a filter element which succeedsthe pickup transducer of the respective transmission line.
 15. Anarrangement for producing artificial reverberation, as claimed in claim11, in which said second filter means, in said second transmission line,includes a high pass filter having a limiting frequency which isapproximately equal to said division frequency.
 16. An arrangement forproducing artificial reverberation, as claimed in claim 11, in whichsaid second filter means, in said second transmission line, suppressestransmission of frequencies outside the range defined between thelimiting frequencies of said first and second springs.